1. Field of the Invention
The present invention relates to a developing apparatus and more specifically to an image forming apparatus that develops an electrostatic latent image on a photoreceptor using a two-component developer including a toner and a carrier.
2. Description of the Related Art
An electrophotographic image forming apparatus that forms an image by an electrophotographic method has been used as an electrostatic copier, a laser beam printer or the like. The electrophotographic image forming apparatus is provided with a developing apparatus for developing an electrostatic latent image formed on an image carrier such as a photoreceptor. As the developing method, a two-component developing method that performs development using a two-component developer (hereinafter, also referred to simply as a developer) containing a toner and a carrier has been known.
In the known two-component developing method, the carrier and the toner are stirred and frictionally charged with one another, and thus, the toner is carried on the surface of the carrier. On a surface of a sleeve containing a magnet, the carrier carrying the toner is formed in a protruding shape called an ear, and a plurality of ears is gathered to form a magnetic brush. When the toner contained in the ears of the magnetic brush moves to the electrostatic latent image on the photoreceptor from the sleeve, the electrostatic latent image is developed.
In order to develop the electrostatic latent image, since there is a need to move the toner contained in the two-component developer stored in the developing apparatus to the photoreceptor as described above, the toner is scattered, the interior of the apparatus is contaminated, or the toner adheres to a portion in which the latent image is not formed, and thus, fog occurs.
In order to prevent scattering of the toner in the developing apparatus, in a developing apparatus disclosed in JP 8-202153 A, a magnetic regulation blade is formed such that an interval between both end portions becomes narrower than an interval in a longitudinal center portion corresponding to an image region.
As a method for preventing the toner scattering from the developing apparatus, there is a method of providing a magnetic member at a position facing both end portions of a developing roller, forming a magnetic brush of the developer between the developing roller and the magnetic member, and performing a seal by the magnetic brush.
Next, in the image forming apparatus, high image quality of an image to be formed is required, and in order to do that, there is a need to perform a thin layer development that further reduces an amount of the developer layer carried on the developing roller surface of the developing apparatus.
In the case of the thin layer development, since an amount of the developer of the developing roller surface is small, even if the magnetic brush for the seal is formed as described above, it is not possible to achieve sufficient seal performance. Also, in the thin layer development, since an interval between the regulation blade and the developing roller surface is small, as in the developing apparatus described in JP 8-202153 A, it is not possible to set the interval at both end portions to be narrower than the interval of the central portion.